A liquid crystal display device is used as a display device such as a high definition color monitor of a computer or other information equipments, a television receiver, or the like. Basically, the liquid crystal display device includes a liquid crystal display portion that has liquid crystal disposed between two substrates, at least one of which is formed by transparent glass or the like. The liquid crystal display device is provided with a driver that selectively applies voltage to pixel electrodes formed on the substrate of the liquid crystal display portion. When the voltage is applied by the driver, pixels of the respective pixel electrodes are controlled.
In general, the liquid crystal display portion is provided with gate signal lines, source signal lines, and pixel electrodes. The gate signal lines respectively extend in a horizontal direction (main scanning direction), and are arranged next to each other in a vertical direction (sub scanning direction), for example. The source signal lines respectively extend in the vertical direction (sub scanning direction), and are arranged next to each other in the horizontal direction (main scanning direction), for example. Thin film transistors (TFTs) and the pixel electrodes are arranged in matrix at intersection points of the gate signal lines and the source signal lines. A gate driver applies voltage (gate signal) to the gate signal lines for turning on and off the TFTs. A source driver applies voltage (source signal) to the source signal lines based on an input image signal to the pixel electrodes, to control transmittance of the liquid crystal that is provided correspondingly to the pixel electrodes, to the value corresponding to the source signal.
In the conventional liquid crystal display device, a difference in waveforms of the source signal may occur depending on positions of the pixel electrodes, even though the source signal having the same level is applied to the pixel electrodes by the source driver. For example, in the pixel electrode that is at a position separated from the source driver, the waveform of the source signal is rounded and becomes a gradually changing waveform, as compared with the waveform in the pixel electrode that is at the position closer to the source driver. Therefore, when the output of the gate signal is finished before the level of the source signal that is applied to the pixel electrode changes to a desired value, the transmittance of the liquid crystal that is provided correspondingly to the pixel electrode may not be controlled to have the desired value. As a result of this, quality of the image to be displayed on the display portion may be deteriorated.
In view of the above, a display device described in Japanese Patent Application Laid-Open No. 2005-140883, for example, employs a precharge mode, in which a signal (precharge voltage) that is higher than a source signal based on the input image signal is applied in the first half of one horizontal scanning period, and the source signal based on the input image signal is applied in the latter half of one horizontal scanning period, so that the level of the source signal to be applied to the pixel electrode changes to the desired value before the output of the gate signal is finished.
According to the display device described in the Japanese Patent Application Laid-Open No. 2005-140883, however, control structure is complicated in order to apply the precharge voltage having the appropriate level according to the position of the pixel electrode.